1. Field of the Invention
The present invention relates to a rear suspension of a vehicle such as an automobile, and more particularly, to a rear suspension for mounting a rear wheel to a vehicle body in a manner of transmitting driving and braking forces therebetween while allowing bounding and rebounding of the rear wheel relative to the vehicle body.
2. Description of the Prior Art
In a vehicle such as an automobile in which a vehicle body is supported on a pair of front wheels and a pair of rear wheels via individual resilient suspension mechanisms, since the center of gravity of the vehicle body is generally above the center of pitching and the center of rolling of the vehicle body, when the vehicle is accelerated the vehicle body pitches rearward so as to lift its front portion and to lower its rear portion, and when the vehicle is braked the vehicle body pitches forward so as to lower its front portion and to lift its rear portion. The former phenomenon is generally called "squatting" and the latter phenomenon is generally called "nose diving". Further, when the vehicle is turning around a corner or along a curved road, the vehicle body rolls sidewardly so that the wheels on the outside of the turning bound and the wheels on the inside of the turning rebound relative to the vehicle body. The squatting and the nose diving are generally uncomfortable to the driver and passengers, and lower the riding quality of the vehicle. The rolling is also generally uncomfortable to the driver and passengers, and also lowers the riding quality of the vehicle. However, if the rolling is too much suppressed by certain suspension control in turning of the vehicle, particularly in turning under braking, the vehicle is apt to spin.
In the conventional double wishbone type suspension, a wheel supporting member such as a spindle or an axle bearing moves along a straight line as seen in a side view of the vehicle in the bounding and rebounding of the wheel relative to the vehicle body. In the conventional trailing arm type suspension, the wheel supporting member moves about a pivot point of the suspension arm positioned on the front side of the center of rotation of the wheel and generally at substantially the same level as or slightly lower than the center of rotation of the wheel. In FIG. 1 of the attached drawing such a trace of movement of the center of rotation A of the wheel is shown for the conventional double wishbone type suspension by a straight line Wa and for the conventional trailing arm type suspension by an arcuate line Ta.
In the geometric analysis of the suspension with regard to the bounding and rebounding of the wheels it is noted that the traces of movement of two points are essential, one being the above-mentioned trace of movement of the center of rotation of the wheel, and the other being the trace of movement of a momentary ground contact point (point B in FIG. 1), that is a point on the wheel at which the wheel contacts the ground at each moment in a standard state of no bounding and no rebounding, these two traces of movement, in combination, determining the center of bounding and rebounding movement of the wheel supporting member relative to the vehicle body (point C in FIG. 1 and called "center of bounding and rebounding" hereinafter). The center of bounding and rebounding coincides with the front pivot point of the arm in the conventional trailing arm type suspension. However, the center of bounding and rebounding can be an imaginary point in the vehicle body through which act the driving and braking forces transmitted between the wheel and the vehicle body. In fact, in the conventional double wishbone type suspension, the center of bounding and rebounding is positioned infinitely forward of the suspension. The driving force applied from the engine to the wheel is reacted by the vehicle body through a line of force passing through the center of rotation of the wheel and said center of bounding and rebounding, while the braking force applied to the wheel is reacted by the vehicle body through a line of force passing through said momentary ground contact point and said center of bounding and rebounding. In FIG. 1, the traces of movement of the momentary ground contact point are shown by lines Wb and Tb for the conventional double wishbone type suspension and the conventional trailing arm type suspension, respectively.
Therefore, by taking the angle of inclination of the line of force in driving, i.e. the angle made by the line passing through the center of rotation and the center of bounding and rebounding with respect to a horizontal line, to be "a" (positive when the point C is higher than the point A), and the angle of inclination of the line of force in braking, i.e. the angle made by the line passing through said momentary ground contact point and the center of bounding and rebounding with respect to a horizontal line, to be "b" (probably always positive), in the rear wheel suspension, the effect of the driving force on the squatting is proportional to tan a, and the effect of the braking force on the nose diving (or a back lifting) is proportional to tan b.
In FIG. 2, the effect of the driving force on the squatting is shown by a one dot line W for the conventional double wishbone type rear suspension and by a broken line T for the conventional trailing arm type rear suspension. Similarly, in FIG. 3, the effect of the braking force on the nose diving is shown by a one dot line W for the conventional double wishbone type rear suspension and by a broken line T for the conventional trailing arm type rear suspension.
The conventional wishbone type rear suspension is, if the inclination is appropriately designed, able to provide a constant anti-squatting effect and a constant anti-nose diving effect regardless of the bounding and rebounding of the wheel relative to the vehicle body. Therefore, however, this type of rear suspension has no effect of suppressing the rolling of the vehicle body in turning of the vehicle, regardless of driving and braking, although it has therefore no adverse effect on it. The conventional trailing arm type rear suspension has a desirable effect of suppressing the rolling of the vehicle body in turning of the vehicle under braking, although too much suppression of the rolling in turning under braking has an adverse effect of increasing the probability of vehicle spinning. However, the rear suspension of this type has an adverse effect on the rolling of the vehicle body in turning of the vehicle under driving, because the balance of the driving forces applied from a pair of rear wheels to the vehicle body always acts to promote the rolling of the vehicle body along with increase of the rolling.